Chronic hyperglycemia is one the main characteristics shared by types 1 and 2 diabetes mellitus. Chronic hyperglycemic levels can result in long term complications, such as increased extracellular matrix (ECM) accumulation, increased collagen crosslinking by Advanced Glycation Endproducts (AGEs), AGE/ Receptor for AGEs (RAGE) cascade activation, and fibroblast to myofibroblast differentiation, which are prime determinants of increased ECM stiffness and ventricular dysfunction. The long term goal of this study is to identify a novel role for Rap1a in type 2 diabetes-mediated ECM remodeling in the heart. The objective of this R15 application is to demonstrate that Rap1a utilizes a PKA-dependent mechanism and a PKA-independent mechanism mediates AGE/RAGE signaling to alter the dynamic plasticity of the heart. The central hypothesis that interrupting Rap1a signaling downregulates type 2 diabetes-mediated AGE/RAGE cascade to reduce fibrotic ECM synthesis and accumulation as preventing maladaptive fibroblast to myofibroblast phenotype differentiation to restore LV structural remodeling and stiffness. The hypothesis is based on a series of preliminary studies demonstrating that left ventricular (LV) collagen levels were significantly decreased in Rap1a knockout mouse hearts, and silencing Rap1a mRNA in diabetic fibroblasts returned collagen expression, myofibroblast differentiation marked by ?-smooth muscle actin, and RAGE expression to that of non-diabetic levels. The rationale for the proposed research is that identifying a cellular and molecular mechanism for Rap1a in AGE/RAGE-mediated myocardial remodeling would provide a unique target for therapeutic strategies aimed at reducing chronic hyperglycemia-mediated ECM production and accumulation in diabetic patients. Three specific aims will critically address this hypothesis: Aim 1 will determine the role of Rap1a signaling in mediating AGE/RAGE cascade activation. Gene ablation of Rap1a in combination with a loss-of-function and gain-of- function strategy will be used to investigate PKA-dependent and PKA-independent changes in ECM and AGE accumulation, RAGE expression, and myofibroblast differentiation in vitro. Aim 2 will determine the role of Rap1a diabetic ECM in mediating myofibroblast differentiation. In vitro 3D ECM matrices isolated from diabetic Rap1a knockout mice to assess Rap1a's impact on ECM mechanical properties and AGE/RAGE-dependent signaling mechanisms of myofibroblast differentiation. Aim 3 will determine the role of Rap1a signaling on the mechanical and biochemical properties of the diabetic mouse heart. LV in vivo functional and structural remodeling, AGE- mediated collagen crosslinking, and basal molecular signaling mechanisms will be evaluated in diabetic Rap1a knockout mice hearts. The research plan present is significant, because it will provide a novel mechanism linking Rap1a to diabetes-mediated ECM remodeling in the heart.